No abstract

The oxidation of used nuclear fuel in a geologic repository has important implications for the mobility of radionuclides and fission products in the environment. Hexavalent uranium (uranyl) minerals, including oxyhydroxides and silicates, form as alteration phases on the surface of fuel pellets in laboratory simulations. However, alpha-radiolysis of water forms hydrogen peroxide in solution, which may favor the alteration of these secondary phases to the uranyl peroxide mineral studtite. This study investigates the alteration of dehydrated schoepite, UO 3 (H 2 O), and soddyite, [(UO 2 ) 2 (SiO 4 )] (H 2 O) 2 , in the presence of aqueous solutions containing hydrogen peroxide. Crystalline samples were reacted with various concentrations of hydrogen peroxide and the resulting material was analyzed by powder X-ray diffraction. Both dehydrated schoepite and soddyite readily convert to studtite in the presence of hydrogen peroxide following the reaction stoichiometry. These results indicate that the possible impact of peroxide buildup on the stability of alteration phases in a repository setting should not be overlooked.

Numerous groundwater sites around the globe have been contaminated by aqueous film forming foam (AFFF) as a result of firefighting, fire training activities and the storage and accidental spillage of AFFF.

Short rotation Eucalyptus plantations offer great potential for increasing wood-fiber production in the southern United States. Eucalyptus plantations can be highly productive (>35 m 3 ha À1 year À1), but they may use more water than intensively managed pine (primarily Pinus taeda L.) plantations. This has raised concern about how expansion of Eucalyptus plantations will affect water resources. We compared tree water use, stem growth, and WUE (kg wood per m 3 water transpired) in adjacent nine-year-old Eucalyptus benthamii and P. taeda plantations with similar stand density and leaf area. Sap flux (F d , g cm À2 s À1) was measured continuously over one year using thermal dissipation probes. Stem biomass, stem growth, tree water use (E t, L day À1), canopy transpiration per unit leaf area (E l , mmol m À2 s À1), and canopy stomatal conductance (G s , mmol m À2 s À1) were quantified. Eucalyptus had higher daily F d (196.6 g cm À2 day À1) and mean daily E t (24.6 L day À1) than pine (105.8 g cm À2 day À1 , 15.2 L day À1). Eucalyptus exhibited a seasonally bimodal pattern in daily E t that did not occur in pine. Monthly E t was 23-51% higher in Eucalyptus and differences between species were greatest in the spring and fall. Annual E t was 32% higher in Eucalyptus (9.13 m 3 H 2 O year À1) than pine (5.79 m 3 H 2 O year À1). Annual stem biomass increment was greater in Eucalyptus (Eucalyptus: 22.9; pine: 11.8 kg tree À1 year À1), and Eucalyptus had greater WUE (Eucalyptus: 2.86; pine 1.72 kg biomass m À3 H 2 O year À1). Pine exhibited a lower seasonal minimum and higher seasonal maximum leaf area index (LAI). At low LAI, there was no significant difference between species in E l or G s ; however, at maximum LAI, pine E l and G s were 46 and 43%, respectively of rates observed in Eucalyptus. The species differed in G s response to vapor pressure deficit (D). At a similar reference G s (G s,ref at D = 1 kPa), pine exhibited greater stomatal sensitivity to D. These results suggest that (1) Eucalyptus trees had higher sap flux and total water use than pine, (2) Eucalyptus had greater stem growth and WUE, and (3) species differences in water use were driven primarily by differences in E l and G s .